The availability of interactive real-time MRI and MR-conditional instruments has lead to an increasing use of MR-guidance especially in transcutaneous procedures performed with needles or linear ablation probes. Besides the lack of ionizing radiation MR-guidance offers a number of advantages for such procedures, the most important one being the soft tissue contrast and full tomographic capability of MR, if compared with CT or US. State-of-the-art clinical MR-guided percutaneous interventions use pre-operative 3D MR images to plan the device path, then stereotactic device guides to align the device with the target and to guide its insertion, which is mostly performed outside the MR bore. Finally, MR is used to confirm that the device has reached the target.
Because stereotactic procedures are prone to registration errors due to patient motion and needle bending, and because they involve a complicated workflow (patient movement into and out of bore), advanced centers are now practicing so-called free-hand procedures, in which the device is advanced without any physical stereotactic device guide under real-time image guidance inside the MR. This is facilitated by dedicated MR sequences that visualize the target lesion and the device with high conspicuity and by the availability of open MR systems.
In Coutts et. at. “Integrated and Interactive Position Tracking and Imaging of Interventional Tools and Internal Devices Using Small Fiducial Receiver Coils,” Magnetic Resonance in Medicine, vol. 40, 1998, pages 908-913, a method of tracking the position of a rigid device within a magnetic resonance scanner is disclosed. The position tracking is performed by means of two or three small magnetic resonance receiver coils attached to individual receiver channels.